High-power semiconductor lasers for applications requiring GHz linewidth source Ivan Divliansky* a , Vadim Smirnov b , George Venus a , Alex Gourevitch a , Leonid Glebov a a CREOL/The College of Optics and Photonics, University of Central Florida, Orlando FL 32816 b OptiGrate, 3267 Progress Drive, Orlando, FL 32826 ABSTRACT In this paper we present the development of semiconductor laser systems with output powers reaching 100 W and linewidths down to 10 GHz. The combination of high power and narrow emission spectrum was achieved through external resonator configurations based on volume Bragg gratings. By using Bragg gratings with extremely narrow spectral selectivity we were able to narrower and lock emission spectra of diode lasers, with precise wavelength tuning achieved by thermal control of the volume grating. The thermal coefficient of our volume gratings was approximately 8 pm/K, which was low enough to guarantee stable frequency operating regime. We implemented successfully two such schemes for lasers generating at 780 nm and 1.55 μm as pumping sources for Rb vapor and Er-doped solid state lasers, correspondingly. Keywords: high-power semiconductor laser, volume Bragg grating, GHz linewidth 1. DEVELOPMENT OF GHZ LINEWIDTH HIGH-POWER LASER SOURCES The last several years, high-power diode lasers are becoming a viable compact alternative of the standard solid-state lasers. To find even broader application several key issues need to be addressed, one of them being the narrowing of the laser emission to GHz linewidths. High-power combined with GHz wide emission spectra have enormous potential in areas of optically pumped alkali-vapor lasers (cesium, rubidium and potassium) and solid state (erbium, thulium) lasers, in Raman spectroscopy and atom cooling [1-3]. Different approaches have been implemented during the years to match the pumping sources emission characteristics to the absorption linewidths of the particular pumped medium. The most widely experimented with are Ti:sapphire, dye and single emitter diode lasers because of their narrow line emission spectra [4-7]. The recent advances in the development of high-quality volume Bragg gratings (VBG) recorded in photo- thermo-refractive (PTR) glass have presented another path for designing and fabricating compact high-power laser systems based upon external cavity locking of single-emitter semiconductor lasers or bars [8-10]. These VBGs have unique properties that make them capable of handling kW range powers and reducing, in the same time, the laser emission spectra down to several or tens of GHz. They also show diffraction efficiencies above 95%, thermal stability up to 400ºC and laser damage threshold of 40 J/cm 2 for 8 ns pulses. Such characteristics make them extremely suitable for high-power laser design schemes. The first system developed was operating at 780 nm and consisted of one diode bar (LaserTel Inc.) with 24 laser diodes (LDs), a fast axes collimator and a feedback element. Each individual LD had 2 mm cavity length and 150 µm aperture width. The laser bar was first collimated in the fast axes and then locked in an external resonator configuration through a volume Bragg grating manufactured by OptiGrate. The VBG used was 18 mm thick and had a diffraction efficiency of 70% for the resonant wavelength. Its spectral and angular selectivity were around 30 pm and 1˚ (FWHM), respectively. The free-running laser diode bar (LDB) had a maximum emission at approximately 780 nm and a spectral width of 5 nm (FWHM). The locking of the LDB through the VBG brought down the emission spectrum to less than 10 GHz width, which was measured by a Fabry-Perot interferometer. If compared to the free-running regime the spectrum was narrowed by 250 times with measured power loss from the VBG of around 10%. High-Power Diode Laser Technology and Applications VII, edited by Mark S. Zediker, Proc. of SPIE Vol. 7198, 71981N · © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.810058 Proc. of SPIE Vol. 7198 71981N-1